CN117063310A - Positive electrode active material and method for preparing same - Google Patents

Abstract

The present application relates to a positive electrode active material capable of realizing a lithium secondary battery having excellent initial charge and discharge efficiency, life characteristics, and thermal stability, wherein the positive electrode active material of the present application comprises: a core portion including a lithium transition metal oxide in which a molar ratio of Ni in all transition metals is 80 mol% or more; and a shell portion of a layered structure formed on the core portion and including a lithium transition metal oxide in which a molar ratio of Mn in all transition metals is 30 mol% or more, and the positive electrode active material satisfies formula 1 described in the present specification.

Description

Cathode active material and preparation method thereof

Technical field

Cross-references to related applications

This application claims priority based on Korean Patent Application No. 10-2021-0061016 filed on May 11, 2020, the entire disclosure of which is incorporated herein by reference.

Technical field

The present invention relates to a positive electrode active material and a preparation method thereof, and more particularly, to a positive electrode active material capable of realizing a lithium secondary battery having excellent initial charge and discharge efficiency, life characteristics and thermal stability and a preparation method thereof.

Background technique

The demand for secondary batteries as energy sources has increased significantly with the increase in demand for mobile devices and electric vehicles, and, among these secondary batteries, lithium secondary batteries with high energy density and low self-discharge rate have been commercialized and being widely used. In particular, demand for high-capacity secondary batteries has increased with the rapid expansion of the electric vehicle market in recent years.

In order to improve the capacity characteristics of secondary batteries, lithium composite transition metal oxides containing two or more transition metals such as NCM and NCMA have been developed and used as positive electrode active materials. In particular, lithium complex transition metal oxides containing a large amount of nickel have been developed and used. However, lithium composite transition metal oxides with high nickel content have problems with poor long-term life and thermal stability.

Generally, during the preparation of lithium composite transition metal oxides such as NCM and NCMA, after preparing a transition metal aqueous solution by dissolving transition metal raw materials such as nickel sulfate, cobalt sulfate and manganese sulfate in water, the transition metal aqueous solution, cation complex The co-precipitation reaction is performed while adding the mixture and the alkaline compound to the reactor at a uniform rate to prepare a transition metal precursor in the form of a hydroxide having a uniform composition inside and outside the particles, and usually by adding the transition metal precursor A lithium composite transition metal oxide having a uniform composition inside and outside the particles is prepared by mixing the body and the lithium raw material and then sintering the mixture. However, it is difficult for conventional lithium composite transition metal oxides prepared by the above method to achieve sufficient life characteristics and thermal stability of lithium secondary batteries.

Therefore, there is a need to develop a positive electrode active material that can realize a lithium secondary battery having excellent life characteristics and thermal stability as well as excellent initial charge and discharge efficiency.

Contents of the invention

technical problem

One aspect of the present invention provides a cathode active material that can realize a lithium secondary battery with excellent initial charge and discharge efficiency, life characteristics, and thermal stability, and a preparation method of the cathode active material.

Technical solutions

In order to solve the above problems, the present invention provides the following positive electrode active material, its preparation method, a positive electrode including the positive electrode active material, and a lithium secondary battery including the positive electrode.

(1) The present invention provides a cathode active material including: a core part including a lithium transition metal oxide in which the molar ratio of Ni in all transition metals is 80 mol% or more; and a layered structure. A shell portion formed on the core portion and containing a lithium transition metal oxide in which the molar ratio of Mn in all transition metals is 30 mol% or more, wherein the positive electrode active material satisfies Formula 1:

[Formula 1]

(2) The present invention provides the cathode active material according to (1) above, wherein the thickness of the shell portion is in the range of 100 nm to 600 nm.

(3) The present invention provides the positive active material according to (1) or (2) above, wherein the average particle diameter (D ₅₀ ) of the positive active material is in the range of 1 μm to 100 μm.

(4) The present invention provides the cathode active material according to any one of (1) to (3) above, wherein the lithium transition metal oxide in which the molar ratio of Ni in all transition metals is 80 mol% or more has Composition represented by Chemical Formula 1.

[Chemical formula 1]

Li _x1 [Ni _a Co _b M1 _c ]O ₂

In Chemical Formula 1,

M1 is at least one selected from Mn, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W, and

0.9≤x1≤1.1, 0.8≤a≤1, 0≤b≤0.2, 0≤c≤0.2, and a+b+c=1.

(5) The present invention provides the cathode active material according to any one of (1) to (4) above, wherein the lithium transition metal oxide in which the molar ratio of Mn in all transition metals is 30 mol% or more has Composition represented by Chemical Formula 2.

[Chemical formula 2]

Li _x2 [Mn _d M2 _e ]O ₂

In Chemical Formula 2,

M2 is at least one selected from Ni, Co, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W, and

0.9≤x2≤1.1, 0.3≤d≤1, 0≤e≤0.7, and d+e=1.

(6) The present invention provides a method for preparing the cathode active material according to any one of (1) to (5) above, which includes the following steps: preparing a precursor for the cathode active material of a multilayer structure, wherein nickel, Two or more elements of cobalt and manganese are precipitated in different areas; and a precursor for a positive electrode active material is mixed with a lithium raw material, and the mixture is sintered.

(7) The present invention provides the method according to the above (6), wherein the step of preparing a precursor for a positive electrode active material includes: adding a metal solution containing nickel and cobalt, an ammonium cation complexing agent and an alkaline compound. A co-precipitation reaction is simultaneously performed to form nickel-cobalt hydroxide particles; and a reaction in which a metal solution containing nickel, cobalt and manganese, an ammonium cation complexing agent and an alkaline compound is added to the nickel-cobalt hydroxide particles. A co-precipitation reaction is carried out simultaneously in the solution to form nickel-cobalt-manganese hydroxide on the nickel-cobalt hydroxide particles.

(8) The present invention provides the method according to the above (6), wherein the step of preparing a precursor for a positive electrode active material includes: adding a metal solution containing nickel, an ammonium cation complexing agent, and an alkaline compound while adding Precipitation reaction to form nickel hydroxide particles; performing a precipitation reaction while adding a metal solution containing manganese, an ammonium cation complexing agent and an alkaline compound to the reaction solution containing nickel hydroxide particles to form manganese therein nickel/manganese hydroxide particles in which hydroxide is precipitated on nickel hydroxide particles; and adding a metal solution containing cobalt, an ammonium cation complexing agent and an alkaline compound to a reaction solution containing nickel/manganese hydroxide A precipitation reaction is performed while in the process to form nickel/manganese/cobalt hydroxide particles in which cobalt hydroxide is precipitated on the nickel/manganese hydroxide particles.

(9) The present invention provides a cathode including the cathode active material according to any one of (1) to (5).

(10) The present invention provides a lithium secondary battery including the positive electrode according to (9).

beneficial effects

The cathode active material of the present invention can improve lithium dielectric performance using the cathode active material by including a shell portion with a high manganese content and adjusting the thickness of the shell portion to an appropriate level relative to the average particle diameter (D ₅₀ ) of the cathode active material. Initial charge and discharge efficiency, long-term life characteristics and thermal stability of secondary batteries.

Description of the drawings

FIG. 1 is a transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDS) mapping image of a cross section of the cathode active material prepared in Example 1.

2 is a TEM-EDS mapping image of a cross section of the cathode active material prepared in Comparative Example 1.

Detailed ways

Hereinafter, the present invention will be described in detail.

It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in commonly used dictionaries, and it should be further understood that the words or terms should be based on the meaning that the inventor can appropriately define the words or terms so as to best The principles that best explain the present invention are to be construed to have meanings consistent with their meanings in the context of the relevant technology and the technical idea of the present invention.

In this specification, the expression "average particle diameter (D ₅₀ )" can be defined as the particle diameter at 50% of the cumulative volume in the particle size distribution curve. The average particle diameter (D ₅₀ ) can be measured using a laser diffraction method, for example. Laser diffraction methods can typically measure particle sizes in the range of a few nanometers to several millimeters and can obtain highly reproducible and high-resolution results.

As a result of extensive research on the development of a positive electrode active material capable of improving the long-term life characteristics and thermal stability of a lithium secondary battery, the present inventors found that the thickness of the shell portion relative to the thickness of the positive electrode active material (the shell portion contained therein) When the average particle diameter (D ₅₀ ) of the cathode active material is adjusted to an appropriate level, the lithium secondary battery using the above positive electrode active material has excellent initial charge and discharge efficiency, long-term life characteristics and thermal stability. This completes the present invention.

positive active material

First, the cathode active material according to the present invention will be described.

The cathode active material according to the present invention includes: a core part including a lithium transition metal oxide in which the molar ratio of Ni in all transition metals is 80 mol% or more; and a shell part of a layered structure, the shell part The portion is formed on the core portion and contains a lithium transition metal oxide in which the molar ratio of Mn in all transition metals is 30 mol% or more, and satisfies the following formula 1.

[Formula 1]

In the present invention, the core part and the shell part can be divided based on the molar ratio of Mn contained in the lithium transition metal oxide. In the lithium transition metal oxide constituting the core, the molar ratio of Ni to all transition metals is 80 mol% or more, and therefore the molar ratio of Mn to all transition metals is 20 mol% or less. Therefore, in the positive electrode active material, a portion in which there is a lithium transition metal oxide with a molar ratio of Mn in all transition metals of 20 mol % or less can be divided into a core portion, and a portion in which Mn is present in all transition metals can be divided into a core portion. The lithium transition metal oxide with a molar ratio of 30 mol% or more is divided into a shell part. The molar ratio of Mn in all transition metals can be confirmed by energy-dispersive X-ray spectroscopy (EDS) mapping or EDS line scanning of a cross section of the positive electrode active material.

The cathode active material according to the present invention is a cathode active material having a different composition between the core part and the shell part, in which the amount of Mn in the constituent elements of the lithium transition metal oxide makes life stability and thermal stability excellent. Concentrated on the surface of particles sensitive to reaction with the electrolyte and functioning as a protective layer, lithium secondary batteries using the above positive electrode active materials have excellent long-term life characteristics and thermal stability.

In the case where the molar ratio of Ni in the lithium transition metal oxide contained in the core part is less than 80 mol%, since the amount of Ni in the entire positive electrode active material is low if the molar ratio of Ni in the shell part is also low, it may It is impossible to prepare a high-capacity lithium secondary battery, and if the molar ratio of Ni in the shell part is high, Mn which is excellent in life stability and thermal stability will not be concentrated on the surface of the positive electrode active material as the purpose of the present invention. on the problem.

In the case where the molar ratio of Mn of the lithium transition metal oxide contained in the shell portion is less than 30 mol%, Mn may not be concentrated on the surface of the positive electrode active material because the Mn content is too low.

The present invention can realize a shell with a completely continuous layered structure by adjusting the thickness of the shell portion with high manganese content so that the thickness of the shell portion is in the range of 0.005 to 0.15 relative to the average particle size (D ₅₀ ) of the cathode active material. department. The value according to Formula 1 may be in the range of 0.005 to 0.15, specifically 0.006 to 0.14. In the case where the thickness of the shell portion is less than 0.005 relative to the average particle diameter (D ₅₀ ) of the cathode active material, since the thickness of the shell portion is too thin compared to the size of the cathode active material, discontinuous islands in the form of islands may be formed. The coating structure (the core part may not be entirely covered), therefore, there is a problem that the thermal stability of the cathode active material is not improved or is poor. In addition, in the case where the thickness of the shell portion is greater than 0.15 relative to the average particle diameter (D ₅₀ ) of the cathode active material, since the thickness of the shell portion is too thick compared to the size of the cathode active material, it is possible only by the growth of manganese A spinel structure is formed, and therefore, there is a problem that the structural stability of the positive electrode active material is deteriorated, and that, for example, when the positive electrode active material is used in a lithium secondary battery, a sudden voltage drop or a deterioration in life characteristics may occur.

According to the present invention, the thickness of the shell portion may be in the range of 100 nm to 600 nm. For example, the thickness of the shell portion may be in the range of 200 nm to 600 nm, or 100 nm to 300 nm. In the case where the thickness of the shell portion is within the above range, the role of the shell portion as a particle protective layer can be optimized.

According to the present invention, the average particle size (D ₅₀ ) of the cathode active material may be in the range of 1 μm to 100 μm. The average particle diameter (D ₅₀ ) of the positive electrode active material may specifically be in the range of 3 μm to 50 μm, for example, 4 μm to 20 μm. In the case where the average particle diameter (D ₅₀ ) of the positive electrode active material is within the above range, the loading amount of the positive electrode active material during preparation of the positive electrode is easily controlled, and the positive electrode active material layer can be formed to have high energy density.

According to the present invention, the lithium transition metal oxide contained in the core part in which the molar ratio of Ni in all transition metals is 80 mol% or more may have a composition represented by the following Chemical Formula 1. In the lithium transition metal oxide contained in the core portion, the molar ratio of Ni to all transition metals is 80 mol% or more, and therefore the molar ratio of Mn to all transition metals is 20 mol% or less.

[Chemical formula 1]

Li _x1 [Ni _a Co _b M1 _c ]O ₂

In Chemical Formula 1, M1 is at least one selected from Mn, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta, and W, and 0.9 ≤x1≤1.1, 0.8≤a≤1, 0≤b≤0.2, 0≤c≤0.2, and a+b+c=1.

M1 may be at least one selected from Mn, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W. M1 may preferably be Mn, Al, Zr or B. In the case where the element M1 is additionally contained, effects such as crystal structure stabilization and surface stabilization can be obtained.

x1 represents the molar ratio of lithium in the lithium transition metal oxide, where x1 can satisfy 0.9≤x1≤1.1, 0.95≤x1≤1.1 or 0.95≤x1≤1.05. When the molar ratio of lithium in the lithium transition metal oxide satisfies the above range, since the layered crystal structure can be well developed, a cathode active material with excellent electrochemical performance can be obtained.

a represents the molar ratio of nickel in the metal components other than lithium in the lithium transition metal oxide, where a can satisfy 0.8≤a≤1, 0.8≤a<1 or 0.85≤a<1. When the molar ratio of nickel satisfies the above range, high capacity characteristics can be achieved.

b represents the molar ratio of cobalt in the metal components other than lithium in the lithium transition metal oxide, where b can satisfy 0≤b≤0.2, 0<b≤0.2 or 0<b≤0.15.

c represents the molar ratio of element M1 in the metal components other than lithium in the lithium transition metal oxide, where c can satisfy 0≤c≤0.2, 0<c≤0.2 or 0<c≤0.15.

According to the present invention, the lithium transition metal oxide contained in the shell part in which the molar ratio of Mn in all transition metals is 30 mol% or more may have a composition represented by the following Chemical Formula 2.

[Chemical formula 2]

Li _x2 [Mn _d M2 _e ]O ₂

In Chemical Formula 2, M2 is at least one selected from Ni, Co, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W, And 0.9≤x2≤1.1, 0.3≤d≤1, 0≤e≤0.7, and d+e=1.

M2 may be at least one selected from Ni, Co, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W. M2 may preferably be Ni, Co, Al, Zr or B. In the case where the element M2 is additionally contained, effects such as crystal structure stabilization and surface stabilization can be obtained.

x2 represents the molar ratio of lithium in the lithium transition metal oxide, where x2 can satisfy 0.9≤x2≤1.1, 0.95≤x2≤1.1 or 0.95≤x2≤1.05. When the molar ratio of lithium in the lithium transition metal oxide satisfies the above range, since the layered crystal structure can be well developed, a cathode active material with excellent electrochemical performance can be obtained.

d represents the molar ratio of manganese in the metal components other than lithium in the lithium transition metal oxide, where d can satisfy 0.3≤d≤1, 0.3≤d<1 or 0.32≤d<1. When the molar ratio of manganese satisfies the above range, thermal stability and long-term life characteristics can be improved.

e represents the molar ratio of element M2 in the metal components other than lithium in the lithium transition metal oxide, where e can satisfy 0≤e≤0.7, 0<e≤0.7 or 0<e≤0.68.

In the positive electrode active material according to the present invention, the Mn concentration is higher at the surface of the positive electrode active material than at the center. Specifically, the molar ratio of Mn in the shell part in all transition metals may be in the range of 30 mol% to 100 mol%, for example, 32 mol% to 100 mol%, and the Mn in the core part is in the range of all transition metals. The molar ratio of may be in the range of 0 mol% to 20 mol%, such as 0 mol% to 15 mol%.

Preparation method of positive active material

Next, the preparation method of the positive electrode active material of the present invention will be described.

The preparation method of a positive active material according to the present invention includes the following steps: (1) preparing a precursor for a multi-layered structure of a positive active material, in which two or more elements of nickel, cobalt and manganese are precipitated in different regions; and (2) ) Mix the precursor for the positive electrode active material and the lithium raw material, and sinter the mixture.

(1) Preparation of precursors for cathode active materials

First, a precursor for positive electrode active materials is prepared with a multilayer structure in which two or more elements of nickel, cobalt, and manganese are precipitated in different regions.

Generally, in order to prepare a precursor for a positive electrode active material containing nickel, cobalt and manganese, the following method is used: a nickel raw material, a cobalt raw material and a manganese raw material are dissolved in a solvent such as water to prepare a metal solution containing nickel, cobalt and manganese, A solution containing nickel, cobalt, and manganese, an ammonium cation complexing agent, and a basic compound are added to the reactor, and a coprecipitation reaction is performed. If the conventional method as described above is used, a nickel-cobalt-manganese hydroxide is prepared in which nickel, cobalt and manganese are distributed in a uniform composition throughout the precursor particles.

On the contrary, the present invention is characterized in that two or more elements among nickel, cobalt, and manganese are contained in different individual solutions, and the precursor for the positive electrode active material is prepared by changing the timing of adding them in the reactor. If the positive electrode active material is prepared by the method according to the present invention, a precursor for the positive electrode active material of a multilayer structure is prepared, in which two or more elements of nickel, cobalt and manganese are precipitated in different regions, and if using as above By using the precursor of the multilayer structure as described above, it is possible to prepare cathode active materials in which the compositions of the core part and the shell part are different.

Specifically, a multilayer structure precursor for positive electrode active materials in which two or more elements of nickel, cobalt, and manganese are precipitated in different regions can be prepared by the following method (I) or (II).

Method (I):

First, a coprecipitation reaction is performed while adding a metal solution containing nickel and cobalt, an ammonium cation complexing agent, and an alkaline compound to form nickel-cobalt hydroxide particles. As described above, if nickel-cobalt hydroxide particles are prepared by co-precipitating nickel and cobalt simultaneously, hydroxide particles having constant concentrations of nickel and cobalt throughout the particles are obtained.

In this case, the co-precipitation reaction can be performed, for example, in the following manner: after performing the reaction for a period of time to form nuclei of hydroxide particles under conditions such that the pH of the reaction solution is in the range of 11.5 to 12.5, preferably 11.8 to 12.3, the reaction is The pH of the solution is adjusted to be lower than the above pH, and the reaction is additionally performed to grow the hydroxide particles.

A metal solution containing nickel and cobalt can be prepared by dissolving a nickel raw material and a cobalt raw material in a solvent such as water.

The nickel raw material can be nickel acetate, carbonate, nitrate, sulfate, halide, sulfide or oxide, and specifically can be NiO, NiCO ₃ ·2Ni(OH) ₂ ·4H ₂ O, NiC ₂ O ₂ ·2H ₂ O, Ni(NO ₃ ) ₂ ·6H ₂ O, NiSO ₄ , NiSO ₄ ·6H ₂ O, nickel halide, or combinations thereof, but the invention is not limited thereto.

The cobalt raw material can be acetate, carbonate, nitrate, sulfate, halide, sulfide or oxide of cobalt metal, and specifically can be CoSO ₄ , Co(OCOCH ₃ ) ₂ ·4H ₂ O, Co( NO ₃ ) ₂ ·6H ₂ O, Co(SO ₄ ) ₂ ·7H ₂ O, or combinations thereof, but the invention is not limited thereto.

If necessary, the metal solution containing nickel and cobalt may further contain a metal solution selected from the group consisting of Mn, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W. of at least one metal.

The ammonium cation complexing agent may be at least one selected from NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ and (NH ₄ ) ₂ CO ₃ , and may The above compound is added to the reactor in the form of a solution in which the compound is dissolved in the solvent. In this case, water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water can be used as the solvent.

The basic compound may be at least one selected from NaOH, KOH, and Ca(OH) ₂ , and may be added in the reactor in the form of a solution in which the above compound is dissolved in the solvent. In this case, water or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water can be used as the solvent.

Next, the addition of the metal solution containing nickel and cobalt is stopped, and the metal solution containing nickel, cobalt, and manganese, the ammonium cation complexing agent, and the alkaline compound are added to the reaction solution containing the nickel-cobalt hydroxide particles. A co-precipitation reaction was carried out simultaneously. As a result, particles in which nickel-cobalt-manganese hydroxide is formed on the nickel-cobalt hydroxide particles are obtained. That is, a precursor for positive electrode active materials of a two-layer structure in which nickel-cobalt-manganese hydroxide coprecipitated on the surface of nickel-cobalt hydroxide particles was prepared.

In this case, the co-precipitation reaction can be performed under conditions where the pH of the reaction solution is in the range of 11.0 to 12.0.

A metal solution containing nickel, cobalt and manganese can be prepared by dissolving a nickel raw material, a cobalt raw material and a manganese raw material in a solvent such as water.

The manganese raw material can be acetate, carbonate, nitrate, sulfate, halide, sulfide or oxide of manganese metal, and specifically can be Mn ₂ O ₃ , MnO ₂ , Mn ₃ O ₄ , MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ ·H ₂ O, manganese acetate, manganese halide, or combinations thereof, but the present invention is not limited thereto.

The nickel raw material, cobalt raw material, ammonium cation complexing agent and basic compound are the same as above.

If necessary, the metal solution containing nickel, cobalt and manganese may further contain a metal solution selected from the group consisting of Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W. of at least one metal.

Method (II):

First, a precipitation reaction is performed while adding a metal solution containing nickel, an ammonium cation complexing agent, and an alkaline compound to form nickel hydroxide particles.

In this case, the precipitation reaction of nickel hydroxide can be performed under conditions where the pH of the reaction solution is in the range of 11.4 to 11.8. When the pH of the reaction solution meets the above range, the precipitation of nickel can proceed smoothly.

The metal solution containing nickel can be prepared by dissolving the nickel raw material in a solvent such as water.

If necessary, the metal solution containing nickel may further contain a metal solution selected from the group consisting of Co, Mn, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W. of at least one metal.

The nickel raw material, ammonium cation complexing agent and basic compound are the same as above.

Next, the addition of the nickel-containing metal solution is stopped, and a precipitation reaction is performed while adding the manganese-containing metal solution, the ammonium cation complexing agent, and the alkaline compound to the reaction solution containing the nickel hydroxide particles to form where Nickel/manganese hydroxide particles with manganese hydroxide precipitated on nickel hydroxide particles.

In this case, the precipitation reaction of manganese hydroxide can be performed under the condition that the pH of the reaction solution is 11.0 or less, preferably in the range of 10.0 to 11.0. When the pH of the reaction solution satisfies the above range, the precipitation of manganese proceeds smoothly.

The metal solution containing manganese can be prepared by dissolving the manganese raw material in a solvent such as water.

If necessary, the metal solution containing manganese may further contain a metal solution selected from Ni, Co, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W. of at least one metal.

The manganese raw material, ammonium cation complexing agent and basic compound are the same as above.

Next, the addition of the metal solution containing manganese is stopped, and a precipitation reaction is performed while adding the metal solution containing cobalt, an ammonium cation complexing agent, and an alkaline compound to the reaction solution containing nickel/manganese hydroxide to form Nickel/manganese/cobalt hydroxide particles in which cobalt hydroxide is precipitated on nickel/manganese hydroxide particles. Through the above method, a three-layer structure of nickel/manganese/cobalt hydroxide can be prepared, in which nickel hydroxide, manganese hydroxide and cobalt hydroxide are precipitated in sequence.

In this case, the precipitation reaction of cobalt hydroxide can be performed under conditions where the pH of the reaction solution is in the range of 11.0 to 11.4. When the pH of the reaction solution meets the above range, cobalt precipitation can proceed smoothly.

The metal solution containing cobalt can be prepared by dissolving the cobalt raw material in a solvent such as water.

If necessary, the cobalt-containing metal solution may further contain a metal solution selected from Ni, Mn, Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W. of at least one metal.

The cobalt raw material, ammonium cation complexing agent and basic compound are the same as above.

A precursor for positive electrode active materials of a multilayer structure in which two or more elements of nickel, cobalt, and manganese are precipitated in different regions can be prepared by method (I) or (II). If the precursor particles grow to a desired particle size, the reaction ends, and the precursor for positive electrode active material is separated from the reaction solution and then dried to obtain the precursor for positive electrode active material.

(2) Mix the precursor for the positive electrode active material and the lithium raw material, and sinter the mixture

Next, the precursor for the positive electrode active material prepared by the above method is mixed with the lithium raw material and then sintered to prepare the positive electrode active material according to the present invention.

Lithium raw materials may include, for example, lithium-containing carbonates (such as lithium carbonate, etc.), hydrates (such as lithium hydroxide hydrate (LiOH·H ₂ O), etc.), hydroxides (such as lithium hydroxide, etc.), nitric acid Salts (such as lithium nitrate (LiNO ₃ ), etc.) and chlorides (such as lithium chloride (LiCl), etc.), and any one thereof or a mixture of two or more thereof may be used.

The mixing of the precursor for the positive electrode active material and the lithium raw material can be carried out by solid phase mixing, and the mixing ratio of the precursor for the positive electrode active material and the lithium raw material can be in a range that satisfies the atomic fraction of each component in the finally prepared positive electrode active material. To be sure within. For example, the precursor for the positive electrode active material and the lithium raw material may be mixed in such an amount that the transition metal:Li molar ratio is 1:0.8 to 1:1.2, preferably 1:0.85 to 1:1.15, more preferably 1:0.9 to 1 : within the range of 1.1. In the case where the precursor and the lithium raw material are mixed within the above range, a positive electrode active material exhibiting excellent capacity characteristics can be prepared.

For reference, for the nickel/manganese/cobalt hydroxide with a three-layer structure in which nickel hydroxide, manganese hydroxide, and cobalt hydroxide are sequentially precipitated, after being mixed with the lithium raw material, cobalt with high diffusivity is easily infiltrated into the particles during sintering to produce a cathode material with a high manganese content on its surface.

Additionally, if desired, materials containing doping elements can be further mixed during sintering. The doping element may be, for example, at least one selected from the group consisting of Al, B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W, and contains the doping element The raw materials can be acetate, sulfate, sulfide, hydroxide or oxyhydroxide containing doping elements.

The sintering may be performed at 600°C to 1,000°C, such as 700°C to 900°C, and the sintering time may be in the range of 5 hours to 30 hours, such as 8 hours to 15 hours, but the invention is not limited thereto.

The present invention may further include the process of mixing raw materials containing coating elements and performing heat treatment after sintering. In this case, the positive active material according to the present invention may be coated with a coating layer.

The metal elements contained in the raw materials containing coating elements may be Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y. The raw material containing coating elements may be acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide containing metal elements. For example, in the case where the metal element is B, boric acid (H ₃ BO ₃ ) can be used.

The coating element-containing raw material may be included in a weight of 200 ppm to 2,000 ppm (0.02 to 0.2 wt%) relative to the lithium transition metal oxide. In the case where the amount of the raw material containing the coating element is within the above range, the capacity of the battery can be improved, and the formed coating can suppress the direct reaction between the electrolyte and the lithium transition metal oxide, thereby improving the long-term performance of the battery. Performance characteristics.

Heat treatment can be performed in the temperature range of 200°C to 400°C. In the case where the heat treatment temperature is within the above range, the coating layer can be formed while maintaining the structural stability of the transition metal oxide. Heat treatment can be carried out from 1 hour to 10 hours. In the case where the heat treatment time is within the above range, an appropriate coating layer can be formed and production efficiency can be improved.

positive electrode

Next, the positive electrode according to the present invention will be described.

The positive electrode according to the present invention includes the above-mentioned positive electrode active material according to the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material according to the present invention.

Since the positive active material has been described above, its detailed description will be omitted, and only the remaining configuration will be described in detail below.

The positive electrode current collector may contain a metal with high conductivity and is not particularly limited as long as it is not reactive within the voltage range of the battery and the positive electrode active material layer is easily adhered thereto. As the positive electrode current collector, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, or the like can be used. In addition, the thickness of the positive electrode current collector is usually 3 μm to 500 μm, and fine unevenness can be formed on the surface of the current collector, thereby improving the adhesion of the positive electrode active material. The positive electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, and the like.

If necessary, in addition to the positive active material, the positive active material layer may optionally contain a conductive material and a binder.

In this case, the positive active material may be included in an amount of 80 to 99% by weight, for example, 85 to 98.5% by weight, relative to the total weight of the positive active material layer. When the cathode active material is contained in an amount within the above range, excellent capacity characteristics can be obtained.

A conductive material is used to provide conductivity to the electrode, where any conductive material may be used without particular limitation as long as it has suitable electron conductivity without causing adverse chemical changes in the battery. Specific examples of the conductive material may be: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber ;Powders or fibers of metals such as copper, nickel, aluminum and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and any one thereof or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the cathode active material layer.

The binder improves the adhesion between the positive active material particles and the adhesion between the positive active material and the current collector. Specific examples of the binder may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethylmethacrylate , carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM , styrene-butadiene rubber (SBR), fluorine rubber, polyacrylic acid, and polymers whose hydrogen is replaced by Li, Na or Ca, or various copolymers thereof, and any one thereof or a mixture of two or more thereof can be used. The binder may be included in an amount of 0.1% to 15% by weight relative to the total weight of the cathode active material layer.

The positive electrode can be prepared according to the conventional preparation method of the positive electrode, except that the above-mentioned positive electrode active material is used. Specifically, the positive electrode active material layer forming composition (positive electrode slurry) prepared by dissolving or dispersing the positive electrode active material and optional binder and conductive material in a solvent is coated on the positive electrode current collector, and then it can The positive electrode was prepared by drying and calendering the coated positive electrode current collector.

The solvent may be a solvent commonly used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or water, and may Use any one thereof or a mixture of two or more thereof. Considering the coating thickness and manufacturing yield of the slurry, if the solvent can dissolve and disperse the cathode active material, conductive material, binder and dispersant, and can provide excellent performance during subsequent coating for cathode preparation For thickness uniformity of viscosity, the amount of solvent used can be sufficient.

In addition, as another method, the positive electrode can be prepared by casting the positive electrode active material layer-forming composition on a separate support, and then laminating the film separated from the support on the positive electrode current collector.

Lithium secondary battery

Next, the lithium secondary battery according to the present invention will be described.

The lithium secondary battery specifically includes a positive electrode, a negative electrode arranged to face the positive electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is the same as the above, a detailed description thereof will be omitted, and only the rest will be described in detail below. structure.

In addition, the lithium secondary battery may further optionally include a battery container housing an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member sealing the battery container.

In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, carbon, nickel, A surface-treated copper or stainless steel such as titanium, silver, and aluminum-cadmium alloys. In addition, the thickness of the negative electrode current collector can generally be 3 μm to 500 μm, and, similar to the positive electrode current collector, fine unevenness can be formed on the surface of the current collector, thereby improving the adhesion of the negative electrode active material. The negative electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, and the like.

In addition to the negative active material, the negative active material layer optionally contains a binder and a conductive material.

A compound capable of reversibly intercalating and deintercalating lithium can be used as the negative electrode active material. Specific examples of negative active materials can be: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; (semi-)metallic materials that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; (semi)metal oxides that may or may not be doped with lithium, such as SiO _β (0<β<2), SnO ₂ , vanadium oxide and lithium vanadium oxide; or a composite containing a (semi)metallic material and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or both of them can be used mixture of the above. In addition, a metallic lithium film can be used as a negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. Typical examples of low-crystalline carbon may be soft carbon and hard carbon, and typical examples of high-crystalline carbon may be irregular, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, condensed graphite, thermal Decomposed carbon, mesophase pitch-based carbon fiber, mesophase carbon microbeads, mesophase pitch, and high-temperature sintered carbon, such as petroleum or coal tar pitch-derived coke.

The negative active material may be included in an amount of 80% to 99% by weight relative to the total weight of the negative active material layer.

The binder is a component that contributes to the adhesion between the conductive material, the active material and the current collector, wherein the binder can generally be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative active material layer agent. Examples of binders may be polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene , polyethylene, polypropylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluorine rubber, and various copolymers.

The conductive material is a component used to further improve the conductivity of the negative active material, wherein the conductive material may be added in an amount of 10% by weight or less, for example, 5% by weight or less relative to the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing adverse chemical changes in the battery, and, for example, a conductive material such as: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black , Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as Zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

For example, the negative electrode active material layer can be prepared by applying a negative electrode active material layer forming composition prepared by dissolving or dispersing an optional binder and a conductive material and the negative electrode active material in a solvent on the negative electrode current collector. on, and the coated negative electrode current collector is dried, or may be prepared by casting the negative electrode active material layer forming composition on a separate support, and then laminating the film separated from the support on the negative electrode current collector .

In lithium secondary batteries, a separator separates the negative electrode and the positive electrode and provides a movement path for lithium ions, wherein any separator can be used as the separator without particular limitation as long as it is commonly used in lithium secondary batteries, especially Therefore, it is possible to use a separator that has a high ability to retain electrolytes and a low resistance to transfer of electrolyte ions. Specifically, porous polymer films may be used, for example, from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene/butene copolymers, ethylene/hexene copolymers, ethylene/methacrylic acid copolymers The prepared porous polymer membrane may have a laminated structure of two or more layers. In addition, a general porous nonwoven fabric may be used, for example, a nonwoven fabric made of glass fiber or polyethylene terephthalate fiber with a high melting point. In addition, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure may optionally be used.

In addition, the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in the preparation of lithium secondary batteries, However, the present invention is not limited to this.

Specifically, the electrolyte may contain an organic solvent and a lithium salt.

Any organic solvent can be used as the organic solvent without particular limitation as long as it can function as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following can be used as the organic solvent: ester-based solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents, such as dibutyl ether or tetrahydrofuran; ketone-based solvents , such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; or carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), carbonate Ethyl ester (EC) and propylene carbonate (PC); alcoholic solvents, such as ethanol and isopropyl alcohol; nitriles, such as R-CN (where R is a linear, branched or cyclic C2-C20 hydrocarbon group, and can including double bonds, aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane; or sulfolane. Among these solvents, a carbonate-based solvent can be used, and, for example, a cyclic carbonate having high ion conductivity and high dielectric constant that can increase the charge and discharge performance of the battery (for example, ethylene carbonate or ethylene carbonate) can be used. propyl ester), and a mixture of low-viscosity linear carbonate compounds (for example, ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate). In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte solution may be excellent.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt may be at least one selected from the following: F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- , and LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiCl, LiI or LiB(C ₂ O ₄ ) ₂ are used as lithium salts. Lithium salts can be used in concentrations ranging from 0.1M to 2.0M. If the concentration of the lithium salt is included in the above range, since the electrolyte can have appropriate conductivity and viscosity, excellent electrolyte performance can be obtained, and lithium ions can move efficiently.

In order to improve the life characteristics of the battery, suppress the decrease in battery capacity, and improve the discharge capacity of the battery, in addition to the above electrolyte components, the electrolyte may further contain at least one additive, such as a halogenated alkylene carbonate compound, For example, difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, ()glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, Sulfur, quinoneimine dyes, N-substituted Azolidinones, N,N-substituted imidazolidines, glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride. In this case, the additive may be included in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics, the lithium secondary battery is suitable for use in portable devices such as mobile phones, notebook computers and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

Therefore, according to another embodiment of the present invention, there are provided a battery module including a lithium secondary battery as a unit cell, and a battery pack including the battery module.

The battery module or battery pack can be used as an electric tool; an electric vehicle, including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or at least one medium and large device in a power storage system power supply.

The shape of the lithium secondary battery of the present invention is not particularly limited, but a cylindrical type using a can, a prismatic type, a bag type, or a coin type can be used.

The lithium secondary battery according to the present invention can be used not only in battery cells used as power sources for small devices, but also as unit cells in medium and large-sized battery modules containing a plurality of battery cells.

Examples of medium and large devices may be electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, but medium and large devices are not limited thereto.

Preferred embodiment

Hereinafter, the present invention will be described in detail based on specific embodiments.

Examples and Comparative Examples

Example 1: Co-precipitation of Ni and Co → Co-precipitation of Ni, Co and Mn

NiSO and _CoSO were added to distilled water in an amount such that the molar ratio of Ni:Co was 95 _: 5 to prepare a first metal solution with a concentration of 2.4M. NiSO ₄ and CoSO ₄ and MnSO ₄ were added to distilled water in an amount such that the molar ratio of Ni:Co:Mn was 61:5:34 to separately prepare a second metal solution with a concentration of 2.4M. In addition, a NaOH aqueous solution with a concentration of 8.0M and an NH ₄ OH aqueous solution with a concentration of 5.1M were prepared.

After placing 18 L of deionized water, 0.025 L of NaOH aqueous solution, and 0.71 L of NH ₄ OH aqueous solution into the reactor, the dissolved oxygen in the water was removed by purging the reactor with nitrogen to form a non-oxidizing atmosphere in the reactor.

Then, while adding the first metal solution at a rate of 5.0 L/hr, the NaOH aqueous solution at a rate of 3.0 L/hr, and the NH ₄ OH aqueous solution at a rate of 0.70 L/hr, at 11.9 The precipitation reaction was carried out at a pH of 0.2 h to form the core of the nickel-cobalt hydroxide particles. Thereafter, after sequentially reducing the stirring speed, adding NaOH, and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first metal solution was added at rates of 5.00L/hr, 3.00L/hr, and 0.70L/hr respectively. , NaOH aqueous solution and NH ₄ OH aqueous solution, a co-precipitation reaction was carried out for 38.2 hours to prepare a core containing nickel-cobalt hydroxide particles.

Thereafter, after stopping the addition of the first metal solution and adding NaOH and adjusting the pH of the reaction solution to 11.4 using a pH sensor, the second metal was added at rates of 5.00L/hr, 3.00L/hr, and 0.70L/hr respectively. solution, NaOH aqueous solution and NH ₄ OH aqueous solution and stirring, a precipitation reaction was performed for 9.6 hours to prepare a precursor for a positive electrode active material, in which nickel-cobalt-manganese hydroxide was precipitated in the core containing nickel-cobalt hydroxide particles. Ministry. The Ni:Co:Mn molar ratio of the entire cathode active material precursor particles is 88:5:7.

Mix the cathode active material precursor prepared as above, LiOH·H ₂ O and Al(OH) ₃ so that the molar ratio of Ni+Co+Mn:Li:Al is 0.98:1.05:0.02 at 765°C It was sintered for 13 hours, ground, washed, and dried to prepare a positive active material. The Ni:Co:Mn:Al molar ratio of the entire cathode active material particles prepared was 86:5:7:2.

Thereafter, 1,000 ppm (0.1 wt%) of H ₃ BO ₃ was mixed with the cathode active material prepared as described above, and heat-treated at 295° C. for 5 hours in an air atmosphere to prepare a B-coated cathode active material.

Example 2: Ni precipitation→Mn precipitation→Co precipitation

_NiSO4 was added to distilled water to prepare a first metal solution with a concentration of 2.4M. Add MnSO ₄ to distilled water to prepare a second metal solution with a concentration of 2.4M. _CoSO4 will be added to distilled water to prepare a third metal solution with a concentration of 2.4M. In addition, a NaOH aqueous solution with a concentration of 8.0M and an NH ₄ OH aqueous solution with a concentration of 5.1M were prepared.

After placing 18 L of deionized water, 0.025 L of NaOH aqueous solution, and 0.71 L of NH ₄ OH aqueous solution into the reactor, the dissolved oxygen in the water was removed by purging the reactor with nitrogen to form a non-oxidizing atmosphere in the reactor.

Then, the first metal solution, NaOH aqueous solution and NH ₄ OH aqueous solution were added at rates of 3.8L/hr, 2.3L/hr and 0.54L/hr respectively to perform the precipitation reaction for 42.2 hours. In this case, the pH of the reaction solution was maintained at 11.6.

Thereafter, after stopping the addition of the first metal solution and adjusting the pH of the reaction solution to the range of 10.8 to 11.0 by adding NaOH and using a pH sensor, the reaction solution was adjusted to 3.8L/hr, 2.3L/hr and 0.54L/hr respectively. The second metal solution, NaOH aqueous solution and NH ₄ OH aqueous solution were added at a speed of 3.4 to 3.4 ℃ to perform the precipitation reaction for 3.4 hours.

Then, after stopping the addition of the second metal solution and adjusting the pH of the reaction solution to 11.4 by adding NaOH and using a pH sensor, the third metal was added at rates of 3.8L/hr, 2.3L/hr, and 0.54L/hr respectively. solution, NaOH aqueous solution and NH ₄ OH aqueous solution, and a precipitation reaction was performed for 2.4 hours to prepare a precursor for a positive electrode active material. The Ni:Co:Mn molar ratio of the entire cathode active material precursor particles is 88:5:7.

Mix the cathode active material precursor prepared as above, LiOH·H ₂ O and Al(OH) ₃ so that the molar ratio of Ni+Co+Mn:Li:Al is 0.98:1.05:0.02 at 765°C It was sintered for 13 hours, ground, washed, and dried to prepare a positive active material. The Ni:Co:Mn:Al molar ratio of the entire cathode active material particles prepared was 86:5:7:2.

Thereafter, 0.1% by weight of H ₃ BO ₃ was mixed with the cathode active material prepared as described above, and heat-treated at 295° C. for 5 hours in an air atmosphere to prepare a B-coated cathode active material.

Example 3: Co-precipitation of Ni and Co → Co-precipitation of Ni, Co and Mn

NiSO and _CoSO were added to distilled water in an amount such that the molar ratio of Ni:Co was 95 _: 5 to prepare a first metal solution with a concentration of 2.4M. NiSO ₄ , CoSO ₄ and MnSO ₄ were added to distilled water in amounts such that the molar ratio of Ni:Co:Mn was 5:5:90 to separately prepare a second metal solution with a concentration of 2.4M. In addition, a NaOH aqueous solution with a concentration of 8.0M and an NH ₄ OH aqueous solution with a concentration of 5.1M were prepared.

After placing 18 L of deionized water, 0.025 L of NaOH aqueous solution, and 0.71 L of NH ₄ OH aqueous solution into the reactor, the dissolved oxygen in the water was removed by purging the reactor with nitrogen to form a non-oxidizing atmosphere in the reactor.

Then, while adding the first metal solution at a rate of 5.00 L/hr, the NaOH aqueous solution at a rate of 3.00 L/hr, and the NH ₄ OH aqueous solution at a rate of 0.70 L/hr, at 11.9 The precipitation reaction was carried out at a pH of 0.2 h to form the core of the nickel-cobalt hydroxide particles. Thereafter, after sequentially reducing the stirring speed, adding NaOH and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first solution was added at a rate of 5.00L/hr, 3.00L/hr and 0.70L/hr respectively. The metal solution, the NaOH aqueous solution and the NH ₄ OH aqueous solution were simultaneously subjected to a co-precipitation reaction for 64.2 hours to prepare a core containing nickel-cobalt hydroxide particles.

Thereafter, after stopping adding the first metal solution and adding NaOH and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first metal solution was added at a rate of 5.00L/hr, 3.00L/hr and 0.70L/hr respectively. While stirring the dimetal solution, NaOH aqueous solution and NH ₄ OH aqueous solution, a precipitation reaction was performed for 5.6 hours to prepare a precursor for the positive electrode active material, in which nickel-cobalt-manganese hydroxide was precipitated in a solution containing nickel-cobalt hydroxide particles. on the core. The Ni:Co:Mn molar ratio of the entire cathode active material precursor particles is 88:5:7.

Mix the cathode active material precursor prepared as above, LiOH·H ₂ O and Al(OH) ₃ so that the molar ratio of Ni+Co+Mn:Li:Al is 0.98:1.05:0.02 at 765°C It was sintered for 13 hours, ground, washed, and dried to prepare a positive active material. The Ni:Co:Mn:Al molar ratio of the entire cathode active material particles prepared was 86:5:7:2.

Thereafter, 0.1% by weight of H ₃ BO ₃ was mixed with the cathode active material prepared as described above, and heat-treated at 295° C. for 5 hours in an air atmosphere to prepare a B-coated cathode active material.

Example 4: Co-precipitation of Ni and Co→Co-precipitation of Ni, Co and Mn

NiSO and _CoSO were added to distilled water in an amount such that the molar ratio of Ni:Co was 95 _: 5 to prepare a first metal solution with a concentration of 2.4M. NiSO ₄ , CoSO ₄ and MnSO ₄ were added to distilled water in amounts such that the molar ratio of Ni:Co:Mn was 61:5:34 to separately prepare a second metal solution with a concentration of 2.4M. In addition, a NaOH aqueous solution with a concentration of 8.0M and an NH ₄ OH aqueous solution with a concentration of 5.1M were prepared.

After placing 18 L of deionized water, 0.025 L of NaOH aqueous solution, and 0.71 L of NH ₄ OH aqueous solution into the reactor, the dissolved oxygen in the water was removed by purging the reactor with nitrogen to form a non-oxidizing atmosphere in the reactor.

Then, while adding the first metal solution at a rate of 5.00 L/hr, the NaOH aqueous solution at a rate of 3.00 L/hr, and the NH ₄ OH aqueous solution at a rate of 0.70 L/hr, at 11.9 The precipitation reaction was carried out at a pH of 0.2 h to form the core of the nickel-cobalt hydroxide particles. Thereafter, after sequentially reducing the stirring speed, adding NaOH and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first solution was added at a rate of 5.00L/hr, 3.00L/hr and 0.70L/hr respectively. The metal solution, the NaOH aqueous solution and the NH ₄ OH aqueous solution were simultaneously subjected to a co-precipitation reaction for 15.4 hours to prepare a core containing nickel-cobalt hydroxide particles.

Thereafter, after stopping adding the first metal solution and adding NaOH and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first metal solution was added at a rate of 5.00L/hr, 3.00L/hr and 0.70L/hr respectively. While stirring the dimetal solution, NaOH aqueous solution and NH ₄ OH aqueous solution, a precipitation reaction was performed for 4.4 hours to prepare a precursor for the positive electrode active material, in which nickel-cobalt-manganese hydroxide was precipitated in a solution containing nickel-cobalt hydroxide particles. on the core. The Ni:Co:Mn molar ratio of the entire cathode active material precursor particles is 88:5:7.

Mix the cathode active material precursor prepared as above, LiOH·H ₂ O and Al(OH) ₃ so that the molar ratio of Ni+Co+Mn:Li:Al is 0.98:1.05:0.02 at 765°C It was sintered for 13 hours, ground, washed, and dried to prepare a positive active material. The Ni:Co:Mn:Al molar ratio of the entire cathode active material particles prepared was 86:5:7:2.

Thereafter, 0.1% by weight of H ₃ BO ₃ was mixed with the cathode active material prepared as described above, and heat-treated at 295° C. for 5 hours in an air atmosphere to prepare a B-coated cathode active material.

Comparative example 1

NiSO ₄ , CoSO ₄ and MnSO ₄ were mixed in distilled water in an amount such that the molar ratio of nickel:cobalt:manganese was 88:5:7 to prepare a metal solution with a concentration of 2.4M. In addition, a NaOH aqueous solution with a concentration of 8.0M and an NH ₄ OH aqueous solution with a concentration of 5.1M were prepared.

After placing 18 L of deionized water, 0.025 L of NaOH aqueous solution, and 0.71 L of NH ₄ OH aqueous solution into the reactor, the dissolved oxygen in the water was removed by purging the reactor with nitrogen to form a non-oxidizing atmosphere in the reactor.

Then, coprecipitation was performed while maintaining the pH of the reaction solution at 11.2 to 11.9 by adding the metal solution, the NaOH aqueous solution, and the NH ₄ OH aqueous solution at rates of 3.8 L/hr, 2.3 L/hr, and 0.54 L/hr, respectively. The reaction was carried out for 48 hours to prepare a precursor for the positive electrode active material. The Ni:Co:Mn molar ratio of the entire cathode active material precursor particles is 88:5:7.

Mix the cathode active material precursor prepared as above, LiOH·H ₂ O and Al(OH) ₃ so that the molar ratio of Ni+Co+Mn:Li:Al is 0.98:1.05:0.02 at 765°C It was sintered for 13 hours, ground, washed, and dried to prepare a positive active material. The Ni:Co:Mn:Al molar ratio of the entire cathode active material particles prepared was 86:5:7:2.

Thereafter, 0.1% by weight of H ₃ BO ₃ was mixed with the cathode active material prepared as described above, and heat-treated at 295° C. for 5 hours in an air atmosphere to prepare a B-coated cathode active material.

Comparative example 2

NiSO and _CoSO were added to distilled water in an amount such that the molar ratio of Ni:Co was 95 _: 5 to prepare a first metal solution with a concentration of 2.4M. NiSO ₄ , CoSO ₄ and MnSO ₄ were added to distilled water in amounts such that the molar ratio of Ni:Co:Mn was 5:5:90 to separately prepare a second metal solution with a concentration of 2.4M. In addition, a NaOH aqueous solution with a concentration of 8.0M and an NH ₄ OH aqueous solution with a concentration of 5.1M were prepared.

After placing 18 L of deionized water, 0.025 L of NaOH aqueous solution, and 0.71 L of NH ₄ OH aqueous solution into the reactor, the dissolved oxygen in the water was removed by purging the reactor with nitrogen to form a non-oxidizing atmosphere in the reactor.

Then, while adding the first metal solution at a rate of 5.00 L/hr, the NaOH aqueous solution at a rate of 3.00 L/hr, and the NH ₄ OH aqueous solution at a rate of 0.70 L/hr, at 11.9 The precipitation reaction was carried out at a pH of 0.2 h to form the core of the nickel-cobalt hydroxide particles. Thereafter, after sequentially reducing the stirring speed, adding NaOH and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first solution was added at a rate of 5.00L/hr, 3.00L/hr and 0.70L/hr respectively. The metal solution, the NaOH aqueous solution and the NH ₄ OH aqueous solution were simultaneously subjected to a co-precipitation reaction for 67.5 hours to prepare a core containing nickel-cobalt hydroxide particles.

Thereafter, after stopping adding the first metal solution and adding NaOH and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first metal solution was added at a rate of 5.00L/hr, 3.00L/hr and 0.70L/hr respectively. While stirring the dimetal solution, NaOH aqueous solution and NH ₄ OH aqueous solution, a precipitation reaction was carried out for 5.3 hours to prepare a precursor for the positive electrode active material, in which nickel-cobalt-manganese hydroxide was precipitated in a solution containing nickel-cobalt hydroxide particles. on the core. The Ni:Co:Mn molar ratio of the entire cathode active material precursor particles is 88:5:7.

Mix the cathode active material precursor prepared as above, LiOH·H ₂ O and Al(OH) ₃ so that the molar ratio of Ni+Co+Mn:Li:Al is 0.98:1.05:0.02 at 765°C It was sintered for 13 hours, ground, washed, and dried to prepare a positive active material. The Ni:Co:Mn:Al molar ratio of the entire cathode active material particles prepared was 86:5:7:2.

Thereafter, 0.1% by weight of H ₃ BO ₃ was mixed with the cathode active material prepared as described above, and heat-treated at 295° C. for 5 hours in an air atmosphere to prepare a B-coated cathode active material.

Comparative example 3

NiSO and _CoSO were added to distilled water in an amount such that the molar ratio of Ni:Co was 95 _: 5 to prepare a first metal solution with a concentration of 2.4M. NiSO ₄ , CoSO ₄ and MnSO ₄ were added to distilled water in amounts such that the molar ratio of Ni:Co:Mn was 68:5:27 to separately prepare a second metal solution with a concentration of 2.4M. In addition, a NaOH aqueous solution with a concentration of 8.0M and an NH ₄ OH aqueous solution with a concentration of 5.1M were prepared.

After placing 18 L of deionized water, 0.025 L of NaOH aqueous solution, and 0.71 L of NH ₄ OH aqueous solution into the reactor, the dissolved oxygen in the water was removed by purging the reactor with nitrogen to form a non-oxidizing atmosphere in the reactor.

Then, while adding the first metal solution at a rate of 5.00 L/hr, the NaOH aqueous solution at a rate of 3.00 L/hr, and the NH ₄ OH aqueous solution at a rate of 0.70 L/hr, at 11.9 The precipitation reaction was carried out at a pH of 0.2 h to form the core of the nickel-cobalt hydroxide particles. Thereafter, after sequentially reducing the stirring speed, adding NaOH and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first solution was added at a rate of 5.00L/hr, 3.00L/hr and 0.70L/hr respectively. The metal solution, the NaOH aqueous solution and the NH ₄ OH aqueous solution were simultaneously subjected to a co-precipitation reaction for 13 hours to prepare a core containing nickel-cobalt hydroxide particles.

Thereafter, after stopping adding the first metal solution and adding NaOH and using a pH sensor to adjust the pH of the reaction solution to 11.4, the first metal solution was added at a rate of 5.00L/hr, 3.00L/hr and 0.70L/hr respectively. While stirring the dimetal solution, NaOH aqueous solution and NH ₄ OH aqueous solution, a precipitation reaction was carried out for 4.8 hours to prepare a precursor for the positive electrode active material, in which nickel-cobalt-manganese hydroxide was precipitated in a solution containing nickel-cobalt hydroxide particles. on the core. The Ni:Co:Mn molar ratio of the entire cathode active material precursor particles is 88:5:7.

Mix the cathode active material precursor prepared as above, LiOH·H ₂ O and Al(OH) ₃ so that the molar ratio of Ni+Co+Mn:Li:Al is 0.98:1.05:0.02 at 765°C It was sintered for 13 hours, ground, washed, and dried to prepare a positive active material. The Ni:Co:Mn:Al molar ratio of the entire cathode active material particles prepared was 86:5:7:2.

Thereafter, 0.1% by weight of H ₃ BO ₃ was mixed with the cathode active material prepared as described above, and heat-treated at 295° C. for 5 hours in an air atmosphere to prepare a B-coated cathode active material.

Experimental example

Experimental Example 1: Checking the composition, average particle diameter, and shell thickness of the positive electrode active material

(1)Average particle size (D ₅₀ )

The average particle diameter (D ₅₀ ) of each cathode active material of Examples 1 to 4 and Comparative Examples 1 to 3 was measured using a particle size distribution measuring instrument (S-3500, Microtrac Corporation), and the results are shown in Table 1 below .

(2)Thickness of the shell

After coating each of the cathode active materials of Examples 1 to 4 and Comparative Examples 1 to 3 with carbon, inspectable particles were prepared by irradiating the sample with an ion beam using a FIB (focused ion beam) instrument (Helios NanoLab 450, FEI Corporation) Cross-section of film sample (thickness approximately 100 nm). The film sample was placed on the grid of a transmission electron microscope (TEM), an energy dispersive X-ray spectroscopy (EDS) mapping image of the cross section of the particle was obtained using TEM (Talos F200X, FEI Corporation), and the presence of Mn in all transition metals was measured. The molar ratio in is 30 mol% or more of the thickness of the portion (shell portion) of the lithium transition metal oxide. The measurement results are shown in Table 1 below. 1 and 2 are respectively TEM-EDS mapping images of the cross-sections of the positive electrode active material particles of Example 1 and Comparative Example 1.

[Table 1]

Experimental Example 2: Evaluation of Initial Charge and Discharge Efficiency and High Temperature Lifetime Characteristics

Each cathode active material, conductive material (FX35), and binder (a mixture of KF9700 and BM730H at a weight ratio of 1.35:0.15) of Examples 1 to 4 and Comparative Examples 1 to 3 were mixed in a weight ratio of 97.5:1:1.5 Mix in N-methyl-2-pyrrolidone (NMP) solvent to prepare cathode slurry. One surface of the aluminum current collector was coated with the positive electrode slurry, dried at 130°C, and then rolled so that the porosity was 24% to prepare each positive electrode.

A Li metal disk was used as the negative electrode.

After preparing the electrode assembly by disposing the separator between the positive electrode and the negative electrode, each lithium secondary battery was prepared by disposing the battery assembly in the battery case and then injecting the electrolyte into the battery case. In this case, as the electrolyte solution, an electrolyte solution in which 1 M LiPF ₆ was dissolved in an organic solvent in which ethylene carbonate:ethylmethyl carbonate:diethyl carbonate was mixed in a volume ratio of 3:3:4 was used.

Each lithium secondary battery prepared as described above was charged to 4.25V at a constant current of 0.1C in constant current/constant voltage (CC/CV) mode (terminal current 0.05C) at 25°C, and then discharged in CC mode. to 3.0V to measure the initial charge and discharge efficiency, repeat the charge and discharge cycle 30 times at a constant current of 0.33C in the range of 3.0V to 4.25V at 45°C to calculate the discharge capacity of the 30th cycle compared with the first The percentage of the discharge capacity of the cycle, as the capacity retention rate (%), is shown in Table 2 below. In this case, 1C=200mA/g.

Experimental Example 3: Thermal Stability Evaluation

After each lithium secondary battery in Experimental Example 2 was charged to 4.25V at a constant current of 0.2C in CC/CV mode (end current 0.05C) at 25°C, the battery was disassembled in the charged state and used with DMC. The positive electrode was washed, the heat flow was measured while increasing the temperature at 10° C./min by using a differential scanning calorimeter (DSC), and the resulting starting point and calorific value are shown in Table 2 below.

[Table 2]

Referring to Tables 1 and 2, it can be confirmed that the core part and the shell part of each cathode active material satisfy the composition according to the present invention, and the ratio of the thickness of the shell part to the average particle diameter (D ₅₀ ) of the cathode active material is in the range of 0.005 to The lithium secondary batteries using the positive electrode active materials of Examples 1 to 4 within the range of 0.15 have better initial charge and discharge efficiency and high temperature life characteristics than the lithium secondary batteries using the positive electrode active materials of Comparative Examples 1 to 3. and thermal stability.

Claims (10)

1. A positive electrode active material, comprising:

a core portion including a lithium transition metal oxide in which a molar ratio of Ni in all transition metals is 80 mol% or more; and

a shell portion of a layered structure, the shell portion being formed on the core portion and including a lithium transition metal oxide in which a molar ratio of Mn in all transition metals is 30 mol% or more,

wherein the positive electrode active material satisfies formula 1:

[ formula 1]

2. The positive electrode active material according to claim 1, wherein a thickness of the shell portion is in a range of 100nm to 600 nm.

3. The positive electrode active material according to claim 1, wherein an average particle diameter (D ₅₀ ) In the range of 1 μm to 100 μm.

4. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide in which a molar ratio of Ni in all transition metals is 80 mol% or more has a composition represented by chemical formula 1:

[ chemical formula 1]

Li _x1 [Ni _a Co _b M1 _c ]O ₂

Wherein, in the chemical formula 1,

m1 is at least one selected from Mn, al, B, mg, ca, ti, V, cr, fe, zn, ga, Y, zr, nb, mo, ta and W, and

x1 is greater than or equal to 0.9 and less than or equal to 1.1,0.8 is greater than or equal to 0 and less than or equal to a is greater than or equal to 1, b is greater than or equal to 0 and less than or equal to 0.2, c is greater than or equal to 0 and less than or equal to 0.2, and a+b+c=1.

5. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide in which a molar ratio of Mn in all transition metals is 30 mol% or more has a composition represented by chemical formula 2:

[ chemical formula 2]

Li _x2 [Mn _d M2 _e ]O ₂

Wherein, in the chemical formula 2,

m2 is at least one selected from Ni, co, al, B, mg, ca, ti, V, cr, fe, zn, ga, Y, zr, nb, mo, ta and W, and

x2 is more than or equal to 0.9 and less than or equal to 1.1,0.3, d is more than or equal to 1, e is more than or equal to 0 and less than or equal to 0.7, and d+e=1.

6. A method of preparing the positive electrode active material of claim 1, the method comprising the steps of:

preparing a precursor for a positive electrode active material of a multilayer structure in which two or more elements of nickel, cobalt and manganese are precipitated in different regions; and

The positive electrode active material precursor is mixed with a lithium raw material, and the mixture is sintered.

7. The method according to claim 6, wherein the step of preparing a precursor for a positive electrode active material comprises:

performing a coprecipitation reaction while adding a metal solution containing nickel and cobalt, an ammonium cation complexing agent and an alkaline compound to form nickel-cobalt hydroxide particles; and

a coprecipitation reaction is performed while adding a metal solution containing nickel, cobalt and manganese, an ammonium cation complexing agent and a basic compound to a reaction solution containing the nickel-cobalt hydroxide particles to form nickel-cobalt-manganese hydroxide on the nickel-cobalt hydroxide particles.

8. The method according to claim 6, wherein the step of preparing a precursor for a positive electrode active material comprises:

performing a precipitation reaction while adding a metal solution containing nickel, an ammonium cation complexing agent and an alkaline compound to form nickel hydroxide particles;

performing a precipitation reaction while adding a manganese-containing metal solution, an ammonium cation complexing agent and an alkaline compound to a reaction solution containing the nickel hydroxide particles to form nickel/manganese hydroxide particles in which manganese hydroxide is precipitated on the nickel hydroxide particles; and

A precipitation reaction is performed while adding a cobalt-containing metal solution, an ammonium cation complexing agent, and an alkaline compound to the reaction solution containing the nickel/manganese hydroxide to form nickel/manganese/cobalt hydroxide particles in which cobalt hydroxide is precipitated on the nickel/manganese hydroxide particles.

9. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 5.

10. A lithium secondary battery comprising the positive electrode of claim 9.